Spinal implant devices and systems are commonly used to correct or stabilize the position of vertebral segments in a patient's back. Such correction may be necessary as a result of accidents, degenerative diseases, etc.
One exemplary spinal implantation system is the CD Horizon® Sextant™ spinal system from Medtronic, Inc. of Minneapolis, Minn., which allows surgeons to deliver and apply screw and rod implants to the posterior aspect of the spine to promote spinal fusion. As discussed in the fact sheet for the Sextant™ system available at http://wwwp.medtronic.com/Newsroom/LinkedItemDetails.do?itemId=1101756222541&itemType=fact_sheet&lang=en_US:                “The CD HORIZON SEXTANT Spinal System is an implant system composed of rods, screws, specially designed surgical tools and a novel mechanical implant delivery device. This device looks much like the sextant of naval navigation, and is the navigation and insertion tool that allows screws and rods to be applied to the spine in a minimally invasive manner.        Two principal elements comprise this device. The first are screw extenders, which are long metal shafts used to deliver and attach screws to the vertebrae through small skin incisions. These extenders protrude outside of the body, allowing the surgeon to arrange and join their ends so that the second principal part, the rod inserter, may be attached. The rod inserter is an arc-shaped arm that swings on an axis and delivers a pre-cut rod through the skin and muscle and into the heads of the implanted screws.”        
Despite the advantages of the Sextant™ system, in some cases it may be difficult for the surgeon to properly align the end of the curved arm of the rod inserter with the screw heads. If the surgeon is ultimately unable to make the proper alignment after repeated attempts, the surgeon has to resort to a traditional surgical approach, which is more invasive to the patient. As a result, the patient is required to be under anesthesia for a longer duration, leading to increased risk of complications and a more difficult recovery.